'95 thunderbird running rough

I just picked up a 95 thunderbird lx with the 4.6 v8, the car had been sitting unstarted for about a year and a half before i got it. when i got it i changed the air filter, changed the oil, put fresh gas in it and put in a new battery. the problem i'm having is when i push the gas about 1/4-1/2 the way down i can rev it to about 4000rpm but if i press it all the way down the lights will dim for a second or two and the rpms will drop to around 1000 and fluctuate between there and around 1500 rpm and it will start backfiring a bunch. what could be causing this?

Welcome to the forum jmiller8973. Do you know if the car ran ok before it was parked for that long? Have you driven it with more then one tankful of gas? There may be some of the old stale gas still mixed with the fresh gas, if not. Add some fuel injector cleaner or something like Seafoam to clean the fuel system. Once you know all of the old gas has been used, a new set of spark plugs should be installed. A new set of plug wires couldn't hurt either. Drive the car normally for a week so the computer can adjust itself and let us know what happens.

first off thank you, the people i got it from said it was running rough before they parked it and they were thinking it was a clogged fuel filter so i replaced the fuel filter, put fuel injector cleaner in and added high octane fuel and after running it a bit its running significantly better. it still sputters a bit if i floor it but if i lift my foot about 1/8th of an inch it runs pretty good